What survives at Croftonpark in County Mayo is a semi-circle, the western portion of what was once a complete circular enclosure, and the missing eastern half had already been levelled before the Ordnance Survey cartographers arrived in 1837. Their six-inch map records only the western arc, which means the destruction took place at some point before the early nineteenth century, leaving behind a site that looks, at first glance, like an incomplete thought.

A rath is an earthen ringfort, the most common monument type in the Irish landscape, typically dating from the early medieval period and used as a defended farmstead. This one was originally enclosed by three concentric earthen banks separated by two ditches, known as fosses, an unusually elaborate arrangement that suggests it was a site of some significance. What remains measures roughly 23 to 25 metres north to south and 18 to 20 metres east to west. The innermost bank has been reduced almost to nothing on its interior face, though it still carries a pronounced external slope. The innermost fosse remains well defined. The second bank, standing to about 1.2 metres externally, is clearer, and fragments of the second fosse and the outermost bank are visible at the south-southwest and north-northwest. The road running along the western side of the site has quietly absorbed parts of the monument over time, with the second fosse truncated where the road passes, and the third bank possibly incorporated into a field fence on the road's western edge. That same road curves in a way that acknowledges the rath's original arc, skirting rather than cutting straight through. On the levelled eastern half, a faint outline of the interior is just discernible at ground level, though no trace of the banks and fosses survives there.

The surviving western banks are thickly covered in brambles and thorn bushes, which both protect and obscure. The interior is under grass. A second enclosure lies roughly 250 metres to the southeast, suggesting this corner of Mayo held more structured settlement than the ordinary pasture surrounding it now implies.